Experimental investigation on vapor injection heat pump with a newly designed twin rotary variable speed compressor for cold regions

•A newly designed twin rotary compressor was adopted in a vapor injection heat pump.•Comparative tests between vapor injection and non-injection cycles were conducted.•System heating capacity was improved by 5.6%–14.4% using injection cycle.•Vapor injection no longer improved the system COP at higher ambient temperatures.

A newly designed twin rotary variable speed compressor was adopted to improve the heating performance of a vapor injection heat pump air conditioner (HPAC) at cold regions in this study. The performances of a R410A HPAC were measured and investigated. The results showed that an optimum intermediate pressure existed to achieve the maximum heating capacity and system COPCOP for the injection cycle, and the heating capacity was enhanced effectively by increasing compressor frequency, however, at the cost of COPCOP decrease. Comparative research on system performances between injection and non-injection cycles indicated that the newly designed compressor could improve the heating performance of the HPAC at low ambient temperatures. Specifically, the system's heating capacity was enhanced by 5.6%-14.4%, and COPCOP improvement reached up to 3.5%. Vapor injection cycle was not suggested at high ambient temperatures due to its lower COPCOP compared with non-injection cycles.